Adhesive, free-standing, partially fluorinated comb copolymer electrolyte films for solid flexible supercapacitors

Solid-state electrolytes exhibiting high safety and flexibility have attracted global attention as an alternative to conventional fluidic and flammable liquid electrolytes for energy storage devices. Herein, we report a free-standing solid electrolyte film with high ionic conductivity, strong adhesive property, and good mechanical strength based on a partially fluorinated, microphase-separated comb copolymer consisting of superhydrophobic poly(2,2,2-trifluoroethyl methacrylate) and amphiphilic crystalline poly(ethylene glycol) behenyl ether methacrylate. The comb copolymer electrolyte film with ionic liquid (IL) exhibited a wide potential window of 2.2 V and retained its excellent flexibility up to 85 wt% IL loading. This property arises from the self-assembled microphase separation, which functions as an effective channel for ion transportation, resulting in improved ionic conductivity. The electrolyte film was applied to a solid supercapacitor with activated carbon electrodes, resulting in a high specific capacitance (37.3 F g⁻¹), energy density (23.2 Wh kg⁻¹), and power density (530 W kg⁻¹), and outperformed the cells made with conventional poly(vinyl alcohol) electrolyte. Interestingly, the fabrication of supercapacitors did not require any separator, adhesive, or packaging process because of the strong self-adhesive and mechanical properties of the comb copolymer electrolyte film.